You can add weight in the following places:
Brass front bulkhead
Brass rear hinge pin brace
Brass under servo mount
Brass under lipo sheet
Of course you could use lead here...
I used brass front bulkhead and rear hinge pin brace. This would be a good start i think. Lipos also vary in weight between specs and mfrs.
Around the 270g mark for a stick pack is nominal. If its under, and you have room, fit some lead or brass sheet under your lipo to bring it up.
If you cant get the brass bulkhead, the under servo weignt is a good alternative.
